Thermal and plasma-enhanced ALD of Ta and Ti oxide thin films from alkylamide precursors

We investigated the thermal and plasma-enhanced atomic layer deposition (PE-ALD) of tantalum and titanium oxides from representative alkylamide precursors, Ta(NMe2)(5) (pentakis(dimethylamino)Ta, PDMAT) and Ti(NMe2)(4) [tetrakis(dimethylamido)Ti, TDMAT]. ALD of Ta2O5 by PDMAT with water or oxygen plasma produced pure Ta2O5 films with good self-saturation growth characteristics. However, incomplete self-saturation was observed for TiO2 ALD from TDMAT. The film properties including microstructure, chemical composition, and electrical properties are discussed focusing on the comparative studies between thermal and PE-ALD processes for both oxides. The results indicate that the PDMAT is a promising precursor for both thermal and PE-ALD of Ta2O5.open117474sciescopu

Debt Crises, Fast and Slow

Drawing on the theory of sovereign risk, we show that, driven by self-fulfilling expectations of default, both slow-moving and rollover (fast) crises are generically possible in models with standard features, at intermediate and high levels of debt, respectively. This is without relying on the specification of debt auctions by Cole and Kehoe (2000). A necessary condition is that debt tolerance thresholds—the time- and state- contingent levels of debt above which default becomes the preferred action by the government—respond endogenously to shifts in investors' expectations. In a sunspot equilibrium, the threat of belief-driven crises may not be enough for the government to deleverage in a recession, and bring debt to default-free levels. Unless the initial debt is close enough to the critical threshold above which the country becomes vulnerable to such crises, the government will keep borrowing, gambling on economic recovery in the future

The effects of nitrogen profile and concentration on negative bias temperature instability of plasma enhanced atomic layer deposition HfOxNy prepared by in situ nitridation

We have prepared plasma enhanced-atomic layer deposition HfOxNy thin films by in situ nitridation using nitrogen/oxygen mixture plasma and studied the effects of nitrogen contents and profiles on the negative bias temperature instability (NBTI). The nitrogen depth profiles and concentrations were controlled by changing the exposure sequences and the nitrogen to oxygen flow ratio, respectively. The best immunity to NBTI degradations was obtained for the nitrogen to oxygen ratio of 2:1 when nitrogen atoms are incorporated away from the high k/Si interface. We propose a dielectric degradation mechanism based on the reaction-diffusion model in which nitrogen plays a role of hydrogen generator at the interface and diffusion barrier in the bulk film. (c) 2008 American Institute of Physics. [DOI: 10.1063/1.2978360]open111012sciescopu

Electrical properties of atomic layer deposition HfO2 and HfOxNy on si substrates with various crystal orientations

The use of high-k gate oxide on Si substrates with alternative orientations is expected to contribute for the fabrication of high mobility devices. In this paper, the interfacial and electrical properties of the plasma enhanced atomic layer deposition (PE-ALD) HfO2 and HfOxNy gate oxides on Si substrates with three different crystal orientations, (001), (011), and (111),were comparatively studied. While PE-ALD HfO2 films were prepared using oxygen plasma as a reactant, PE-ALD HfOxNy films were prepared by in situ nitridation using oxygen/nitrogen mixture plasma. For all crystal orientations, in situ nitridation using oxygen/nitrogen mixture plasma improved electrical properties producing lower leakage currents and smaller equivalent oxide thickness values. Both HfO2 and HfOxNy films have shown the lowest leakage current and interface state density on Si (001), whereas the poorest electrical properties were obtained on Si (111). The results are discussed based on the experimental results obtained from various analytical techniques, including I-V, C-V, conductance methods, and X-ray photoelectron spectroscopy. (C) 2008 The Electrochemical Society.open111818sciescopu

Atomic scale nitrogen depth profile control during plasma enhanced atomic layer deposition of high k dielectrics

Nitrogen incorporation produces several benefits in the performance of high k gate oxides. However, since too much nitrogen incorporation at the interface of gate dielectric can result in device degradation, the atomic scale control of nitrogen depth profile is desirable. In this study, the authors have improved electrical properties and interface properties by depth profile control of in situ nitrogen incorporation during plasma enhanced atomic layer deposition. The best electrical properties in terms of hysteresis, equivalent oxide thickness, and interface states were obtained when the nitrogen is incorporated in the middle of the thin film, which has not been achievable by other techniques.open111719sciescopu

Interspecific competition underlying mutualistic networks

The architecture of bipartite networks linking two classes of constituents is affected by the interactions within each class. For the bipartite networks representing the mutualistic relationship between pollinating animals and plants, it has been known that their degree distributions are broad but often deviate from power-law form, more significantly for plants than animals. Here we consider a model for the evolution of the mutualistic networks and find that their topology is strongly dependent on the asymmetry and non-linearity of the preferential selection of mutualistic partners. Real-world mutualistic networks analyzed in the framework of the model show that a new animal species determines its partners not only by their attractiveness but also as a result of the competition with pre-existing animals, which leads to the stretched-exponential degree distributions of plant species.Comment: 5 pages, 3 figures, accepted version in PR

Atomic layer deposition of Ta-based thin films: Reactions of alkylamide precursor with various reactants

The growth mechanisms and film properties of atomic layer deposition (ALD) Ta-based thin films were investigated from alkylamide precursor [Ta(NMe2)(5), (PDMAT)]. The reactions of PDMAT with various reactants including water, NH3, Oxygen, and hydrogen plasma were studied and the resulting film properties were investigated by various analysis techniques. For TaN ALD from NH3 and H plasma, the films were contaminated by considerable amount of carbon, while the Ta2O5 deposited from water and O plasma were quite pure. Also, nitrogen was incorporated for ALD from PDMAT and H plasma, while no nitrogen incorporation was observed for O-plasma based plasma enhanced-ALD of Ta2O5 except at high deposition temperature over 300 degrees C. The results were comparatively discussed focusing on the differences in growth mechanism depending on reactants. (c) 2006 American Vacuum Society.open113639sciescopu

Electrical property improvements of high-k gate oxide by in situ nitrogen incorporation during atomic layer deposition

Atomic layer deposition (ALD) process for oxynitrides of high-k gate dielectrics employing NH4OH as a single source for reactants, water and NH3, was studied. By this method, nitrogen was incorporated up to 1-3 at. % for ALD Al2O3 and Ta2O5 films from metal organic precursors. A comparative study with water based ALD showed that the electrical properties were improved. The leakage current of oxide films from NH4OH based ALD had been reduced and, more importantly, the dielectric strength was found to be enhanced by more than two orders of magnitude from a time dependent dielectric breakdown measurement. (c) 2007 American Institute of Physics.X119sciescopu